Altimetric type measurement method for use on a satellite
An altimetric type measurement method for use on a satellite transmits a pulse towards the surface of the sea and carries out frequency transformation on the return signal resulting from the reflection of this pulse at the surface of the sea. This produces a spectral signal of samples successively comprising:(a)--a first zone with a low amplitude level,(b)--a second zone with a sharply increasing slope ending at a peak, and(c)--a third zone of decreasing slope.Samples of the spectral signal are selected within a selection zone that corresponds to the first and second zones for a predetermined maximal level of the height of the waves at the surface of the sea and maximum likelihood processing is applied only to the selected samples.
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Claims
1. An altimetric type measurement method for use on a satellite and comprising the steps of:
- transmitting measurement pulses towards the surface of the sea,
- frequency transformation of a resultant signal resulting from the reflection of said pulses at the surface of the sea into a spectral signal of samples successively comprising:
- (a)--a first zone with a low amplitude level corresponding to a thermal noise level,
- (b)--a second zone with a sharply increasing slope ending at a peak and dependent on the height of the waves at the surface of the sea, a back-scattering coefficient and the altitude of said satellite, and
- (c)--a third zone of decreasing slope associated with depointing of an antenna of the measuring device, and
- estimating from said samples of said spectral signal, by means of maximum likelihood processing using a model ignoring depointing of the antenna, at least one of the following values: the height of the waves at the surface of the sea, the back-scattering coefficient and the altitude of the satellite,
- in which method samples of said spectral signal are selected within a selection zone that corresponds to said first and second zones for a predetermined maximal level of the height of the waves at the surface of the seal said maximum likelihood processing being applied only to the selected samples.
2. The method claimed in claim 1 wherein said measurement pulses are frequency modulated and said frequency transformation step is preceded by a step of mixing a frequency modulated reference pulse with each of said frequency modulated measurement pulses received after reflection at said surface of the sea to produce said resultant signal.
3. The method claimed in claim 1 including selection of samples of said spectral signal in a this selection zone that corresponds to said third zone for predetermined maximal level of the height of the waves at the surface of the sea and measuring depointing of said antenna as a function of the decreasing slope of said spectral signal in said third selection zone.
4. The method claimed in claim 1 wherein samples of said spectral signal are selected in a first selected zone that corresponds to said first zone for predetermined maximal level of the height of the waves a the surface of the sea and said thermal noise level is measured as a function of the mean level of said selected samples from said first selection zone.
5. The method claimed in claim 1 wherein said spectral signal of samples is tracked so as to center it in the frequency window of said frequency transform.
6. The method claimed in claim 5 wherein said tracking is effected so that the number of samples of said spectral signal in said first selection zone is minimal.
7. An altimeter type measuring device for use on a satellite, including:
- means for transmitting measurement pulses towards the surface of the sea,
- means for frequency transformation of a resultant signal resulting from the reflection of said pulses at surface of the sea to produce a spectral signal of samples successively comprising:
- (a) a low amplitude level first zone corresponding to a thermal noise level,
- (b) a second zone with a sharply increasing slope ending at a peak and dependent on the height of the waves at the surface of the sea, a back-scattering coefficient and the altitude of said satellite, and
- (c) a decreasing slope third zone associated with depointing of an antenna of said measuring device and,
- means for estimating from said samples of said spectral signal, by means of maximum likelihood processing using a model ignoring depointing of said antenna, at least one of the following values: the height of the waves at the surface of the sea, the back-scattering coefficient and the altitude of the satellite, the device further including means for selecting samples of said spectral signal in a selection zone that corresponds to said first and second zones for a predetermined maximal level of the height of the waves at the surface of the sea and said maximum likelihood processing being applied only to these selected samples.
8. The device claimed in claim 7 wherein said pulses transmitted are frequency modulated and further including means for mixing a frequency modulated reference pulse with each of said frequency modulated measurement pulses received after reflection at the surface of the sea to produce said resultant signal.
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Type: Grant
Filed: Feb 21, 1997
Date of Patent: Jul 13, 1999
Assignee: Alcatel Espace (Nanterre Cedex)
Inventors: Sophie Gouenard (Toulouse), Laurent Rey (l'Union)
Primary Examiner: John B. Sotomayor
Law Firm: Sughrue, Mion, Zinn, Macpeak & Seas PLLC
Application Number: 8/804,378
International Classification: G01S 1326;
